Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$84.26	8.131%	$91.1112	$91.11	$91.10	$91.10
Purchase #2	$126.83	12.478%	$142.6558	$142.66	$142.65	$142.70
Purchase #3	$127.40	8.607%	$138.3653	$138.37	$138.35	$138.40
Purchase #4	$39.78	13.125%	$45.0011	$45.00	$45.00	$45.00
Purchase #5	$127.77	3.209%	$131.8701	$131.87	$131.85	$131.90
Purchase #6	$40.29	12.655%	$45.3887	$45.39	$45.40	$45.40
Purchase #7	$106.48	13.254%	$120.5929	$120.59	$120.60	$120.60
7 purchase totals =	$652.81		$714.9851	$714.99	$714.95	$715.10